Wireless communications systems provide wireless service to a number of wireless or mobile units situated within a geographic region. The geographic region supported by a wireless communications system is divided into spatially distinct areas commonly referred to as “cells.” Each cell, ideally, may be represented by a hexagon in a honeycomb pattern. In practice, however, each cell may have an irregular shape, depending on various factors including the topography of the terrain surrounding the cell. Moreover, each cell is further broken into two or more sectors. Each cell is commonly divided into three sectors, each having a range of 120 degrees, for example.
A conventional cellular system comprises a number of cell sites or base stations geographically distributed to support the transmission and reception of communication signals to and from the wireless or mobile units. Each cell site handles voice and/or data communications within a cell. Moreover, the overall coverage area for the cellular system may be defined by the union of cells for all of the cell sites, where the coverage areas for nearby cell sites overlap to ensure, where possible, contiguous communication coverage within the outer boundaries of the system's coverage area.
Each base station comprises at least one radio and at least one antenna for communicating with the wireless units in that cell. Moreover, each base station also comprises transmission equipment for communicating with a Mobile Switching Center (“MSC”). A mobile switching center is responsible for, among other things, establishing and maintaining calls between the wireless units, between a wireless unit and a wireline unit through a public switched telephone network (“PSTN”), as well as between a wireless unit and a packet data network (“PDN”), such as the Internet. A base station controller (“BSC”) administers the radio resources for one or more base stations and relays this information to the MSC.
When active, a wireless unit receives signals from at least one base station over a forward link or downlink and transmits signals to at least one base station over a reverse link or uplink. Several approaches have been developed for defining links or channels in a cellular communication system, including time division multiple access (“TDMA”), frequency division multiple access (“FDMA”), orthogonal frequency division multiple access (“OFDMA”) and code division multiple access (“CDMA”), for example.
Wireless communication is supported by an increasing number of frequency bands in the RF spectrum. At least 10 frequency bands ranging from about 450 MHz to about 2000 MHz have presently been allocated for wireless cellular communication. The rights to use carrier frequencies within each band of this spectrum have been awarded historically to wireless service providers by governmental bodies, such as the Federal Communications Commission in the United States, for example, through mostly auction. Over the past decade, however, a number of wireless service providers have merged and/or acquired. Consequently, a smaller number of larger wireless service providers exist today some of which own successor rights to a number of carrier frequencies in a number of frequency bands.
Presently, each base station supporting CDMA technology, for example, may transmit at least one (e.g., a set) overhead message over the paging channel. These overhead messages provide each potential wireless unit with a suite of information including a channel list message and/or an extended channel list message. The channel list message lists the availability of carriers in a single frequency band. In response, the wireless unit may select an available carrier in a single frequency band listed in the channel list message randomly using a hashing algorithm. Since support for a given frequency band by a wireless unit may be optional, the wireless unit may select a different carrier depending on the set of frequency bands supported thereby.
For example, wireless technology standard IS-2000 calls for a hashing algorithm to enable a wireless system supporting multiple carriers to achieve statistical load-balancing and maximize system capacity without compromising performance. The hashing algorithm may be employed to uniformly distribute wireless access across a number of carrier frequencies within a single band. The uniform distribution of wireless access may be derived from the number of carriers listed in the channel list message, as well as an identifier for each wireless unit.
The existing applications of hashing algorithms, however, have a number of limitations. Firstly, hashing algorithms may not be applied to wireless access over a number of carriers over multiple frequency bands. As a consequence, multi-carrier load balancing may be more difficult to realize in cell sites supporting more than one frequency band. Moreover, hashing algorithms may not be applied to support steering types of services, such as voice or data, for example, or identified wireless units to a desired carrier(s). Hashing algorithms may not also support a uniform distribution of carrier usage based on the services supported by each available carrier.
Consequently, a need exists of enhancing the application of hashing algorithms in wireless communication systems. A demand exists for a method of applying a hashing algorithm to wireless access over a number of carriers over multiple frequency bands. A need further exists for a method of applying a hashing algorithm to support steering wireless access to a desired frequency carrier(s) based on traffic and/or system load or volume, types of services, and/or wireless unit identification. There also exists a demand for a method of applying a hashing algorithm that supports a uniform distribution of carrier usage based on the services supported by each available carrier.